Thanks so much for explaining. Screaming for 23 out of 24 hours a day -- WOW! Of course, that is not meant as aggression on her part; she is expressing her own pain, not being aggressive. But what a lot of pain. It makes sense that something is beyond the range of usual here -- either inutero drug exposure, or even abuse in the first week of her life, as you say.
I have worked with kids who were exposed to drugs in utero, and in those cases it almost certainly affected brain development and caused lags in emotional regulation. And if there are genetic mental health issues, those could show up fairly early.
But I don't believe people are born with in an "angry" or "defiant" personality. I think she may be genetically and biologically inclined toward reactivity and fear, which produces aggressive behavior. I do encourage you to check out Hand in Hand, as I mentioned in my last answer to you, which specifically helps kids who are lashing out, and which also supports parents. I'm sure you can use all the support you can get, although you've already earned your angel wings just from the first months of screaming.
I'm also concerned that she hasn't progressed in speech. She might well need more than speech therapy -- some additional testing. I don't think genetic testing would give you much info, because the expression of genes is often determined by environment.
As far as parenting practices go, you obviously have a VERY challenging child, so compassion and empathy are critical, along with limits as necessary. In addition to reading the Aha! Parenting website, if you haven't already, and Hand in Hand.org, I would also recommend that you read Heather Forbes' books.
And, crucially, make sure to get yourself some support. You are doing very hard work.